In power systems transmission and distribution, protection plays a central role for disturbance-free power supply. Power systems are required to have protective elements like the circuit breakers (CB) in order to ensure isolation of circuits in case of faults. The faults are usually short-circuits involving two or three phases, with or without the ground. FIG. 1 shows the schematic of a power transmission system 100. The transmission line is represented using a series resistor-inductor (R-L) circuit 102, the power generator as the voltage source (e(t)) 104, and the circuit breaker is represented as a switch (SW) 106. During normal operation, the switch is normally closed (NC) to ensure load current flow. In the event of a fault, high current flows through the circuit, so the switch is opened to isolate the circuit, which is also termed as “breaking”.
The fault current has high magnitude. For example, in high voltage (HV) transmission, which typically involves more than 65 kV, the fault current may be typically about 100 kA or more. For medium voltage (MV) transmission, which is typically less than 35 kV, and low voltage (LV) transmission, which is typically less than 1 kV, the fault current may range from about 10 kA to about 50 kA. Such high current is detrimental for the whole power system, and should be isolated as fast as possible. Electrically isolation may be achieved by separating the poles of the circuit breaker (CB).